1. Field of the Invention
The invention relates to any field of application using processing that necessitates the reception of linearly polarized beams. In particular, the invention can be used in array antenna beam-shaping and aiming systems that use delay generation with polarization switching.
Unlike the generation of phase shifts between the elements of an array antenna, the generation of true delays gives an aiming direction that does not depend on the frequency.
Microwave delays can be created by optical means. The use of optics to convey microwave signals gives devices that have low dependency on the electrical frequency conveyed. These properties are especially valuable in electronic scanning antennas that have to work in a wide frequency band. Furthermore, devices using optics have reduced mass and space requirements.
2. Description of the Prior Art
Multiple devices for the creation of microwave delays by optical means are known.
The patent Thomson-CSF FR 2659754 proposes a device of this kind using polarization switches. FIG. 1 gives a schematic view of an example of this multiple device 5 for the creation of delays (hereinafter called a multiple delay-correction device) using polarization switches CPi (1xe2x89xa6ixe2x89xa6n). Delays in several parallel optical paths can be commanded by means of polarization switches CPi consisting for example of matrices of pixels such as spatial light modulators, liquid crystal matrices, etc. Since the optical carriers are modulated by microwave signals, the delays will also be applied to these signals.
The association of several switches CPi consisting of pixel arrays, polarization splitter/recombiner elements SPi and reflector elements Ri achieve the quantified control of the delay of each optical channel. Indeed, by controlling each pixel of a given polarization switch Cpi, the delay that will be undergone by each path at the crossing of the assembly [Spi, Ri] (direct or delayed route) is determined in binary fashion.
This concept has the advantage of providing for a multiple processing of the different spatially separated optical channels.
FIG. 2 shows a possible implementation of a multiple delay-creation device 5 using prior art polarization switches CP. This exemplary application is the supply of an antenna array working in transmission (with beam-shaping at transmission).
A modulated optical source 1 gives a beam to the coupler 2. The coupler 2 maintains the polarization and distributes the entering beams to the polarization-maintaining fibers 3M. These beams are transmitted by the fibers 3M though the array of lenses 4M to the multiple delay-creation device 5 using polarization switches CP. The processed beams (delayed or not) at output of the multiple delay-creation device 5 are transmitted to the photodetectors 6 through the array of lenses 4V and the optical fibers 3V for which the maintaining of the polarization is not necessary. The array of lenses 4M and 4V provide for accurate coupling between the fibers 3M and 3V respectively and the multiple delay-creation device 5. Each photodetector 6 is connected to an antenna element or sub-array 7.
In order that the selection of a delay by polarization switching may be efficient, the polarization switch must receive a linearly polarized beam. This is why the implementation of the multiple delay-creation device 5 with polarization switches CPi described in the patent FR 2659754 requires polarization-maintaining elements 2 and 3M upline from the multiple delay-creation device 5. This constraint is not negligible because these polarization-maintaining elements, couplers 2 for example, of the fibers 3M are more costly and more difficult to implement than elements that do not maintain polarization.
The present invention is used to overcome or at least reduce these drawbacks by proposing an alternative solution.
It proposes a system comprising a processing device that necessitates the reception of linearly polarized beams at input wherein it furthermore comprises at least one element for polarization splitting in open space, placed upline from said device.
This system may comprise for example:
a polarization switch downline from said device, and
an element for superposing polarization in open space downline from the polarization switch.
The invention furthermore proposes a method comprising a step for the processing of linearly polarized beams, the method comprising at least the splitting of polarizations in open space achieved prior to said processing step.
This method for example comprises the following steps:
an additional polarization switching achieved after said processing step, and
the superposing of polarization in open space achieved after said additional switching step.